The present invention relates to a method of manufacturing liquid crystal cell, and more particularly to a simplified method of manufacturing the wide viewing angle liquid crystal cell.
A liquid crystal display device(LCD) which records and processes an optical information basically comprises two substrates, and a liquid crystal between them. In the LCD, it is essential to arrange a liquid crystal director to obtain uniform brightness and high contrast ratio.
Direction of the liquid crystal director is controlled by a variety of process after an alignment layer is formed by depositing polymer on the substrate.
Namely, a coordinate n of the nematic liquid crystal director in cartesian coordinate of FIG. 1 is controlled by determining an alignment direction .theta. and a pretilt angle .phi. on the alignment layer as follows.
n=(cos .theta.cos .phi., cos .theta.cos .phi., sin .theta.)
Recently LCDs used in potable televisions or notebook computers require large size. A twisted nematic liquid crystal display(TN-LCD) has a narrow viewing angle ie., the transmittance in each grey level depends on the viewing angle. This viewing angle dependence, specially, is very strong in the up and down directions. This angular dependence in the up and down directions is caused by the electrically induced liquid crystal(LC) director configuration.
FIG. 2 is drawing showing a structure of the liquid crystal cell having the alignment restricting power, liquid crystal molecules are twisted to right-handed direction by that.
The TN-LC cell is characterized in that the transmittance in each grey level depends on the viewing angle.
FIG. 3a is a graph showing a relationship between transmittance and voltage, FIG. 3b is a graph showing a relationship between transmittance and viewing angle in X-X' direction(right-left direction) of FIG. 2, and FIG. 3c is a graph showing a relationship between transmittance and viewing angle in Y-Y'(up-down direction) direction of FIG. 2.
As shown in FIGS. 3a through 3c, while the transmittance in X-X' direction is symmetrically distributed, the transmittance in Y-Y' direction is asymmetrically distributed as a result, the wide viewing angle can not be achieved by the gray inversion in Y-Y' direction.
To solve the above discussed problem, a multi-domain LCD has been introduced as shown in FIG. 4 and FIG. 5.
FIG. 4 a drawing showing a structure of a two-domain TN LCD(TDTN LCD). Two alignments 26 having a plurality of pretilt angles is formed on each substrate 21, 22. When a voltage is applied to the cell, each of the liquid crystal directors is located at opposite directions as a result, the transmittance is compensated and the wide viewing angle is achieved.
Further, FIG. 5 is a drawing showing a structure of a domain divided TN-LCD(DDTN LCD). A first alignment layer 27 and a second alignment layer 28 are formed on two substrates 21, 22, each alignment layer may be organic or inorganic alignment layer. Here, each alignment layer has a different pretilt angle to divide a domain in a single pixel, thereby the wide viewing angle is achieved.
In addition, a four-domain TN LCD using the pixel dividing method provides a improved viewing angle characteristic.
An inverse direction rubbing method as shown in FIGS. 6a through 6e have commonly been used to obtain the multi-domain LC cell.
Firstly, a mono-domain is completed as shown in FIG. 6b by rubbing a substrate 21 on which a polyimide 22 is deposited as shown in FIG. 6a. After blocking the domain with a photoresist 23 as shown in FIG. 6c, rubbing is executed in the opposite direction to form the opposite alignment direction as shown in FIG. 6d. Further the photoresist 23 is removed. As a result, as shown in FIG. 6e, the substrate 21 is divided into two domains wherein each domain has a different pretilt angle.
In addition, FIGS. 7a through 7f represent a photo-alignment method. Firstly, a first alignment direction is decided by vertically irradiating the linearly polarized light having a first polarization direction on a photo alignment material-coated substrate as shown in FIG. 7a. A first pretilt angle is decided by inclined irradiation of the linearly polarized light as shown in FIG. 7b. After removing a mask to decide a pretilt angle direction of the blocked domain in FIG. 7a, the domain having the first pretilt angle is blocked with a mask. A second alignment direction is decided by vertically irradiating the light having vertical polarization direction against the first polarization direction as shown in FIG. 7d. A second pretilt angle is decided by inclined irradiation of the linearly polarized light to decide a pretilt angle direction in the second alignment direction. When the photoresist is removed, it is possible to provide a two-domain divided substrate as shown in FIG. 7f.
In the related art, however, a plurality of complex processes are required. Also in order to provide the four-domain LC cell, double process are required. Namely, in the alignment process of a multi-domain cell such as a two-domain cell, however, since eight exposure processes and four masking processes are needed, the overall process is complicated with an increased cost.